Materialism

The belief that only matter exists.  Mind or consciousness is (somehow) reducible to matter, its properties, or interactions.

Mechanism

The view that all phenomena can be explained using the principles by which machines are explained:  classical physics and chemistry, and mechanical science.  The 17th-century mechanists—Galileo, Boyle, Descartes, Hobbes, and Newton among others—advanced the theory of mechanism to eliminate all non-observable and mathematically untreatable explanations, in particular vitalistic and teleological explanations.  While mechanism has been extremely successful in terms of epistemological clarity and technical application, it has been criticized for unduly reducing the richness and complexity of life to a few basic entities and forces.

Mendelian inheritance

As opposed to extrachromosomal inheritance, the pattern of gene inheritance, first described by Gregor Johann Mendel, in which one copy of a gene (allele) is inherited from each parent by an offspring.

Metaphysics

The philosophical study of the most general or abstract characteristics of reality:  identity, existence, substance; permanence and change, time and space, cause and effect, difference and sameness, unity and variety, mind and matter, and so forth.

Microcosm/macrocosm

Literally “small-order”/”large-order,” the very old and very common belief, found in both Western and Eastern cultures, that parts of the human body correspond to aspects of the universe, that every part mirrors the whole, or that the microcosm corresponds to the macrocosm.  Variations on this theme include the analogy between the human being and society, and between society and the universe.  Since the Renaissance, the microcosm/macrocosm analogy has largely been displaced by a mechanistic, ontologically-materialistic model of the universe.